Hello Fadi,
Maybe you have not fully understood the concept of combo. A combo product is just the presentation of a list of products you can choose. For instance, you make a menu: entrée, main dish, desert
In this case, you first have to create all the entrées, all the main dishes and all the deserts as products.
Then you create the combo product menu with the choices entrée containing the list of all entrées choices you want to offer, main dishes and deserts.

I would discourage you from using variants to describe the products.
2. If you want you can add a product with the name large. You will not have so many different products.
3. You can either have a combo choice with adds-on or use kitchen notes from the POS to specify to take something away.

You will probably have to create all those products. After this the inventory is always automatically updated whenever you sell anything, provided, it is defined as inventory relevant.
Regards
eva P.
I think you don't understand the difference between a combo product and a variable product also.
Thanks for your reply